The effect of the number of insemination on the fertility of mares inseminated three times/week (Monday, Wednesday and Friday), with extended, cooled and transported semen, from only one stallion, was studied. The mares were inseminated from the detection, by rectal palpation, of a 3.0 to 3.5 cm follicle diameter, in one of the ovaries, until ovulation. The semen was transported in skim milk-glucose extender in a "Celle" modified container; with inseminate doses of 400 x 106 motile spermatozoa at the moment of the final dilution, before cooling. The results of 148 cycles of 100 mares were grouped, in accordance with the number of artificial inseminations (AI), in: 1AI, 2AI, 3AI and 4 or more AI. The pregnancy efficiency was 4.29; 5.04; 5.67 and 3.43 to groups 1, 2, 3 and 4 or more, respectively. The follicular characteristics were different according to insemination frequency with the greatest values observed on the group of 4 or more times inseminated mares. The results of this experiment permit to conclude that a slow follicular growth speed and the biggest ovulatory follicular diameter were associated with a greater number of artificial insemination /cycle. Moreover, with an appropriate spermatic concentration, the insemination number/cycle have no influence upon fertility.